1. Field of the Invention
The present invention relates to a novel surface-roughened film and sheet comprising a polymer of 4-methyl-1-pentene, and a process for the production and use thereof.
2. Description of the Related Art
The essentially non-oriented surface-roughened film and sheet of the present invention is especially useful for the production of multilayer printed circuit boards, which are increasingly used in various kinds of electric apparatus. Usually, in a manufacturing process for multilayer printed circuit boards, first, single-sided metal-clad laminates or double-sided metal-clad laminates are produced and then an electric circuit is printed on those laminates, and the printed circuits are stacked via prepregs and pressed with heating to form the multilayer printed circuit boards. To strengthen the adhesion between the resin side of the single-sided metal-clad laminates and the prepregs, the surface of the resin side of the single-sided metal-clad laminate is preferably surface-roughened.
The above-mentioned single-sided or double-sided metal-clad laminate is manufactured by stacking a metal foil and a prepreg, and pressing them with heating to harden the prepreg. In such procedure, to surface-roughen the surface of the resin side of the laminate, a surface-roughened film or sheet is applied to a surface of the prepreg during the hardening process.
The surface-roughened film and sheet according to the present invention is useful as the above-mentioned surface-roughened film to roughen the surface of the resin side of the single-sided metal-clad laminate.
Japanese Examined Patent Publication No. 52-34664 discloses a process for the production of a biaxially oriented film having frosted surfaces comprising methyl-pentene polymer, which process comprises biaxially orienting a film comprising methylpentene polymer, high-density polyethylene and polystyrene, and heat-hardening the resulting film to form a frosted film. However the publication does not disclose the use of the film having frosted surfaces to surface-roughen the surface of the resin side of a laminate.
Japanese Examined Patent Publication No. 52-49823 discloses a process for the production of a laminate by an additive process characterized by placing a releasing film having a surface roughness of 0.5 to 5.mu. on a prepreg impregnated with a thermoset resin, and forming it with heating. However the publication discloses only a triacetate film for the releasing film.
Japanese Unexamined Patent Publications No. 57-70653, No. 58-163648, and No. 57-70654 describe the use of 4-methylpentene-1 sheet as a releasing film in the manufacture of a laminate from a prepreg and metal foil. But these publications do not disclose the use of a surface-roughened film as a releasing film.
As a film providing roughness to the above-mentioned multilayer circuit board, TEDLAR (Trade mark of Du Pont, USA) a biaxially oriented film of polyvinyl fluoride containing a substantial amount of low molecular fillers and 5% calcium carbonate is commercially available. Since, however, this film is produced by biaxial orientation, the surface thereof has deposits of the low molecular materials and calcium carbonate thereon. Therefore, when this film is used to produce single-sided metal clad-laminates by alternately stacking the copper foil and a prepreg, and the TEDLAR film between the layers of the copper foil and the prepreg, and pressing them with heating to harden the prepregs, the low molecular materials and the calcium carbonate may be transferred to the surface of the laminated copper foil, resulting in unsatisfactory adhesion between the copper surface and a resist, and unsatisfactory etching during further processing of the multilayer circuit boards.
Triacetylcellulose films having a surface roughened by sandblasting have been used. But, in this case, the fine sand and cellulose cause the same problems as mentioned above for TEDLAR.